Cons: Doesn’t provide a legitimately cleaner signal than the iPod musters on its own, either adding or dramatically amplifying high-pitched static; only of potential use to those with extremely low-efficiency headphones, which are neither popular nor typically used with an iPod.

Some iPod accessories are made for the masses. Others are made primarily for narrow audiences. Simpl Acoustics’ A1 audio amplifier for the iPod ($149.99) is a prime example of the latter: it boosts the iPod’s headphone jack output from Apple’s ear-splitting (and internationally illegal) loudest setting to “why would anyone ever need so much volume?” loud. So if you’re not an audiophile, and haven’t needed extra headphone jack power from your iPod, you’ll probably want to stop reading right now.

Once audiophiles get past the initial question of whether the iPod is sufficiently capable of accurately reproducing audio (it is), their next foci are how to make the most of the hardware’s headphone port and Dock Connector line output. Though ninety-five percent (or more) of iPod owners will never notice the difference, harder-core audiophiles prefer audio from the iPod’s Dock Connector to that of its headphone jack. They believe that the iPod’s built-in amplifier has the potential to distort the original audio signal, and would sooner hear clean, unamplified output from the Dock Connector port. The only problem is that headphones can’t plug into the Dock Connector port - you’d need to dock your iPod, and then, you’d probably want to use speakers instead of headphones anyway. Audiophiles have come up with workarounds, but they’re frequently impractical.

Simpl Acoustics is offering a solution of sorts for these audiophiles. The A1 audio amplifier is a full-sized iPod-matching small white plastic backpack with rubberized grips that fit all current-model and third-generation iPods. It includes its own amplifier circuitry, a rechargeable battery with mini USB connection (and LED light) for computer-aided recharging, a white power button and green LED power light, and ports to connect headphones to amplifier, then amplifier to iPod. Small white packed-in cables perform the amplifier to iPod connection and A1-to-computer recharging connections; not surprisingly, you provide your own headphones.

The one missing feature: a volume knob. Simpl multiplies whatever volume the iPod is set on, and since the Dock Connector port’s line-out audio is at a constant (and high) volume, even the aforementioned audiophile workarounds won’t help you to practically connect the A1 to the Dock Connector and headphones. Therefore, the A1’s only usable with the iPod’s headphone port, nothing more.

Connecting the A1 to the iPod is effortless; the A1’s eight rubberized pads guarantee that its white plastic body won’t scratch the iPod’s chrome back, and once attached, it’s easy enough to intentionally remove. Despite its lack of an active locking mechanism of any sort, in our testing, it didn’t fall off accidentally - a good design.

Pressing the power button yields an instant and dramatic increase in the iPod’s volume level. Most of our favorite earphones yield clear, listenable audio at the iPod’s 50% volume mark, give or take 10% depending on the specific earphones and ambient conditions. When the A1 is plugged in, the iPod’s 50% volume setting becomes roughly equivalent to its 100% volume level, and every step above 50% cranks the volume further above dangerous listening levels - for normal earphones at least. When the iPod’s set on 70% with the A1 attached, typical earphones sound like small speakers from a distance - a setting that will rapidly drain your iPod’s battery while blowing out your ears and your earphones. At 100%, you can hear massive distortion from a distance - you’d never want to have your ears anywhere close to most earphones even at the A1’s 50% setting.

What’s the purpose of such amplification? In theory, if you don’t believe that the iPod’s built-in amplifier can increase the volume of music past a certain point without distorting it, you turn the iPod to an acceptably undistorted volume level and use the clean A1 amplifier to boost the volume of the clean iPod sound. Or, if you’re using a really serious pair of headphones - huge, high-quality but low-efficiency earcups - you may need the A1’s extra juice to provide extra power to your listening devices. Finally, you could use the A1 to reduce the minimal iPod battery drain caused by typical headphones.

Low-volume testing didn’t show the A1 to be especially useful under the first theory. When we tested the A1’s amplification with Etymotic ER-4P and Ultimate Ears UE-10 Pro earphones at the iPod’s 15% volume level, we noticed that the iPod’s amplified signal didn’t sound better than it did at the iPod’s 50% volume with the A1 turned off. In fact, a faint high-pitched static sound was present and noticeable in the amplifier at low volume levels, but not audible in the iPod’s original, unamplified signal. Putting the faint high-pitched sound aside, the bass-friendlier UE-10 Pros did show a fair bit of bass boost that wasn’t as noticeable in the ER-4Ps, but you’ll need to have and like bass-heavier headphones to appreciate this difference. Harder-core audiophiles generally prefer their sound clean and accurate, and the iPod does this quite well without any amplifier if you have efficient portable earphones.

That leaves the A1’s other purposes: extra juice for hulking headphones, or extra juice for typical headphones. The latter purpose isn’t realistic - you won’t buy one of these over a comparably priced battery pack just to modestly improve the iPod’s battery performance. But if you have a huge pair of headphones that you need to power, the A1 provides a convenient, iPod-matching way to do it. The unit’s built-in rechargeable battery gives you roughly ten hours of assisted play time before it needs to be plugged into a computer, though the number will vary based on how much current your headphones draw.

Overall, the A1’s utility isn’t quite what it could be - it sets out to solve an audio problem that typical users feel that the iPod doesn’t have, and introduces its own high-pitched issue in the process - at least, at low volumes, and with good headphones. Since it’s intended to be used at reasonable volumes with good headphones, we don’t see the point, except for bass-heads with an extra $150 to toss around. While we commend Simpl Acoustics on the physical design and overall functionality of the A1, it’s not the sort of add-on we’d recommend to most of our readers. We’d sooner spend the cash on better headphones, and use iTunes EQ settings to achieve the same bass boost.

Jeremy Horwitz is Editor-in-Chief of iLounge.

Editors' Note: iLounge only reviews products in "final" form, but many companies now change their offerings - sometimes several times - after our reviews have been published.
This iLounge article provides more information on this practice, known as revving.